كتب : Omar AbdelAziz
The result means that Adelaide will meet African champions Ahli in the 5th place playoff match on Thursday.
Gamba registered their third victory over the Oceania side this season, following a 5-0 aggregate victory in the AFC Champions League final.
The only goal of the game came from Yasuhito Endo after 23 minutes, finishing off a magnificent team move signified by a classy heading assist by substitute Ryuji Bando.
Gamba were lucky not to concede an equalizer before half-time, when Adelaide captain Travis Dodd was denied by the bar.
Dodd almost grabbed a last-gasp equalizer, but his close-range header went inches wide.
The Japanese claimed the narrow win and set up a semi-final tie with European champions Manchester United.